The conversion of penicillin sulfoxides to desacetoxy cephalosporins has been accomplished in poor yield in refluxing toluene or xylene in the presence of an acid such as p-toluene sulfonic acid or acetic anhydride. Morin et al., U.S. 3,275,626. Analogous processes are disclosed in U.S. Pat. Nos. 3,647,787; 3,668,202; and Belgium Pat. Nos. 747,119, 747,120 and 763,104. The reaction has been considered to proceed through cleavage of the sulfurcarbon bond of the thiazolidine ring of penicillin to afford an unsaturated sulfenic acid, and possibly an intermediate anhydride or protonated sulfenic acid, which ring closes with the olefinic unsaturation to form a sulfonium ion, the latter being subject to attack by an anion to open the sulfonium ring in the production of a cephalosporin derivative or a substituted penam system. Barton et al., J. Chem. Soc. (London) (C), pp. 3540-3550 (1971). It is known that isothiazoles result from treatment of a penicillin sulfoxide ester with triethylamine or pyridine Morin et. al. J.A.C.S. 91, 1401 (1969); Barton et. al., supra at page 3542.